Recently, the demand for improvements in photographic silver halide emulsions has become pronounced, and further, requirements have also been demanded for higher level photographic performance including higher speed, higher contras, superior process stability and pressure resistance.
The use of tabular silver halide grains as means for enhancing the sensitivity of silver halide emulsion and in particular for enhancing the quantum sensitivity thereof are described in U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306 and 4,459,353; JP-A 58-111935, 58-111936, 58-111937, 58-113927 and 59-99433 (herein, the term, JP-A means a unexamined, published Japanese Patent Application). Techniques of introducing dislocation lines are generally known as a means for enhancing sensitivity and graininess. U.S. Pat. No. 4,956,269, for example, discloses the introduction of dislocation lines into tabular silver halide grains.
The tabular grain technique described above is effective to achieve enhanced sensitivity of silver halide emulsions. However, when the dislocation lines are applied to silver halide grains having a high aspect ratio (i.e., a ratio of grain diameter to grain thickness) to make the most of desired characteristics of the tabular grains, it was found that deterioration was caused in other photographic performance such as contrast, process stability or pressure resistance.
It is commonly known that application of pressure to silver halide grains causes fogging or desensitization. However, there was a problem that dislocation lines-introduced grains exhibited marked desensitization when subjected to pressure.
JP-A 59-99433, 60-35726 and 60-147727 disclose techniques for improving pressure characteristics using core/shell type grains. JP-A 63-220238 and 1-201649 disclose techniques for improving graininess, pressure characteristics and exposure temperature dependence as well as sensitivity by introducing dislocation lines into silver halide grains. Further, JP-A 6-235988 discloses a technique for enhancing pressure resistance by use of multilayer-structured, monodisperse tabular grains having a high iodide-containing intermediate shell.
Photogr. Sci. Eng. 18, 215-225 (1974) disclosed that cubic silver halide grains exhibited little desensitization in inherent sensitivity and high contrast when a sensitizing dye was allowed to be adsorbed thereon. However, specifically in the case of cubic grains, cubic grains containing 5% or less chloride, it was difficult to prepare completely cubic grains. Herein completely cubic grains refers to cubic-formed grains having overall external faces substantially formed of (100) faces. Accordingly, incompletely cubic grains refers to grains having external faces other than (100). In most cases, the face index other than (100) is (111) or (110) faces. In fact, such silver halide grains having external faces of plural face indexes are different in the face proportion from each other.
As a result of studies by the inventors of the present invention, it was found that a reduced variation coefficient of the proportion of (100) face among grains led to improvements in sensitivity, contrast and process stability, specifically when being subjected to reversal development. An adverse effect, due to a broad distribution of the face proportion is a difference in quantum sensitivity for each grain and it is contemplated to result in reduced contrast or reduced quantum sensitivity of overall silver halide grains. However, influences thereof have not definitely known.
It was further found that the broad distribution of the face proportion is not advantageous in terms of process stability and such non-advantageous effects were marked in development processing employing solution physical development. Examples thereof include a development process of color reversal photographic materials. It is assumed that variation in dissolution of silver halide grains is a phenomenon due to differences in stability in the developer between surfaces of different face indexes of the grain and non-uniformity among grains with respect to coverage of an adsorbing substance such as a sensitizing dye.
JP-A 5-341417 discloses that a high proportion of (100) faces is effective in enhancing performance, but there is nothing described with respect to effects of the distribution of the face proportion per grain among grains.
It was further found by the present inventors that a silver halide grain emulsion containing 5 mol % or less chloride and 0.5 mol % or more iodide, in which at least 50% of the total grain projected area was accounted for by regular crystal grains of at least 50% of the (100) face proportion for each grain and a coefficient of variation of the (100) face proportion among grains exhibited enhanced sensitivity, higher contrast and superior process stability.
JP-A 5-107670, 4-317050, 5-53232, 4-372943 and 4-362628 disclose techniques for introducing dislocation lines into regular crystal grains. However, it was proved that these techniques did not reach levels of recent requirements for higher sensitivity, higher contrast and improved process stability and pressure resistance.
In addition, it was found that forming an internal band-formed layer containing high iodide within the grain (hereinafter, also called high iodide contour) led to enhanced sensitivity and localization of the high iodide layer, resulting in improved pressure resistance. It was also proved that uniformity in crystal habit of the grain external faces was an important factor for enhancing uniformity among grains and achieving enhanced sensitivity, contrast and process stability. In the case of regular crystal grains, and specifically, in the case of cubic grains containing 5 mol % or less chloride, however, it is difficult to make the crystal habit of the grain external face uniform among the grains. Besides the (100) face, in most cases, a (111) or (110) face is present. In fact, such silver halide grains having external faces of plural face indexes were different in the face proportion from each other.
It was further found by the present inventors that a silver halide emulsion containing silver halide regular crystal grains having dislocation lines, in which a variation coefficient of the number of the dislocation lines among grains was 30% or less and when an outermost layer of the grain was present, led to superior performance in sensitivity, contrast and process stability, specifically when subjected to reversal development. It was further found that silver halide grains which included a small internal high iodide portion by volume within the grain, exhibited superior pressure resistance as well as enhanced sensitivity. JP-B 6-14173 (herein, the term, JP-B means a published Japanese Patent) discloses octahedral silver halide grains containing internally a high iodide layer. However, these grains are entirely different from those of the present invention with respect to the position of the high iodide layer and the crystal habit of the grains, and the effect thereof concerns an improvement in pressure fogging so that any effect of the present invention cannot be expected therefrom. It was also found that in silver halide grains, when the dislocation lines were orientated in the direction toward the corners or edges of the cubic grains or toward the grain surface of the (111) or (110) face, sensitization effects were further enhanced. The effects of the present invention were marked in color reversal photographic materials which were subjected to color reversal processing.